<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div class="a">
    <p>1</p>
    <p>2</p>
    <p>3</p>
    <p>4</p>
    <p>5</p>
    <p>6</p>
    <p>7</p>
    <p>8</p>
    <p>9</p>
</div>
<div class="b">
    <p>10</p>
    <p>11</p>
    <p>12</p>
    <p>13</p>
    <p>14</p>
    <p>15</p>
    <p>16</p>
    <p>17</p>
    <p>18</p>

</div>
<div class="c">
    <p>19</p>
    <p>20</p>
    <p>21</p>
</div>
    <style>
          div{width: 800px;
        height: 71px;;
        margin: auto;
    left: 50%;
    top: 50%;}
        .b{text-align: center;
        line-height: 50px;
        color: rgb(241, 239, 236);
        font-size: 20px;
         display: flex;}
        .a{text-align: center;
        line-height: 50px;
        color: rgb(241, 239, 236);
        font-size: 20px;
         display: flex;}
         .c{text-align: center;
        line-height: 50px;
        color: rgb(241, 239, 236);
        font-size: 20px;
         display: flex;}
        p:nth-child(2n+1){  width: 50px;
            height: 50px;
            background-color: rgb(42, 11, 244);
            border-radius: 50%;
            border: 5px solid ;
            border-color: rgb(240, 9, 9);
            border-width: 5px;
            text-align: center; 
        margin-left: 10px;}
        p:nth-child(2n){  width: 50px;
            height: 50px;
            background-color: rgb(0, 0, 0);
            border-radius: 50%;
            border: 5px solid ;
            border-color: rgb(240, 9, 9);
            border-width: 5px;
            text-align: center;
        margin-left: 10px;}
    </style>  
</body>
</html>